Wikipedia describes reactive programming as “a programming paradigm oriented around data flows and the propagation of change”. This description already gets to the core of what reactivity in the context of programming means. Now, the additional attribute “functional” in FRP as opposed to just reactive programming can [...] simply refer to a “programming paradigm for reactive programming using the building blocks of functional programming” [...]. We also note that FRP libraries differ from “non-functional” reactive libraries in that the former almost always provide functional combinators to manipulate reactive constructs and strive to be more declarative in general.
[...] We sum up that in this thesis we understand FRP as a paradigm around data flows, change propagation and time-varying values or event-streams using functional building blocks.
via: Eugen Kiss (2014): "Comparison of Object-Oriented and Functional Programming for GUI Development", http://www.eugenkiss.com/projects/thesis.pdf